Ink jet is a computer-to-print technology in which digital signals drive droplets of ink through a print head and then directly onto a substrate. The print head may consist of one or more nozzles through which ink droplets are ejected and directed onto the substrate. Ink jet printing differs from other plate-less digital technologies, like copier or toner-based technologies (e.g., as employed in desktop printer applications), because it is non-contact—the printing device never comes into direct contact with the substrate. While employed in consumer applications, ink jet printers are also well suited for various industrial and commercial uses, wherein variable, high speed printing or on-demand print handling capability is necessary.
One primary cause of ink jet printing problems is due to ink drying on the print head's nozzles, causing the pigments and dyes to dry out and form a solid block of hardened mass that plugs the microscopic ink passageways. When this occurs, the expected ink output markings to be applied to the substrate are compromised, often appearing, if at all, as faded, smeared, incomplete, jagged, disoriented, etc. Such occurrences, wherein the appearance of the printed output as placed onto the intended substrate is poor, is considered poor print quality. Obviously, this is not the preferred outcome, particularly in instances where high volumes of documents, packages, or other print items of various substrates are required to be produced with specific print markings. If the exemplary print quality defects described above are discovered too late, additional time, materials and effort must be further employed in reprinting the defective items.
Various methods are employed today for identifying print quality issues. For example, clogged nozzles can be detected by periodically printing a test print item (e.g., a page of a document) and verifying the print item for quality. Another method is to intentionally print a known pattern onto a select portion of a print item in process and subsequently verifying the pattern for quality. Instances where the pattern or markings do not exhibit quality—i.e., the actual printed markings differ from the intended print markings—highlights an occurrence of print quality failure. Identification and verification of such failures may be performed through the usage of an imaging system, which may include a camera device and select pattern recognition software (e.g., OCR or image recognition software).
While these methods and accompanying tools may be effective, they do not address instances of erroneous print quality verification, and particularly, those instances wherein a print quality failure is erroneously determined due to inaccurate verification. This is common in instances where the substrate upon which the print item is to be composed includes various inherent characteristics that may affect the verification process. For instance, consider a document printing job that requires the generation of hardcopy documents onto a particular pre-printed stock paper. If the verification process does not account for the presence of pre-existing print markings resident upon the paper stock in advance, print quality failure will be the natural result. This would be the only logical conclusion of the imaging system, as additional patterns (the pre-existing markings) besides the actual printed markings would appear on the document subsequent to print. Even if pre-existing markings were accounted for in advance by the verification system, accurate print quality failure could be hampered by the presence of paper creases, folds, wrinkles, grease marks, paper fibers, unintended ink blots and other such inherent qualities of the stock paper.
For the reasons stated above, a method and system for improved print verification is needed. Such improved technology, for example, should account for both pre-existing print markings and inherent qualities of a particular substrate, to enable accurate print verification.